With OS X Mountain Lion, Apple no longer maintains active support for Sync Services. You might experience issues, if you are using Sync Services to sync your Outlook data - calendar, contacts, tasks, and notes - with local applications and smart phones, like iPhone, iCal and RIM.

This occurs when both Outlook and the email server are adding copies of the messages to the Sent Items folder after they are sent. To fix this, go to Outlook > Preferences > Accounts > select the IMAP account > Advanced > Folders and select Don't store a copy of sent messages.

Duplicate emails display for Gmail accounts

This is due to a conflict with Gmail's All Mail folder. If you have rules running on your Gmail account, it's recommended that you remove them from Outlook and create them from Gmail's web interface. You can also unsubscribe from the All Mails folder by going to Tools > IMAP Folders > [Gmail] / All Mail and click Unsubscribe.

MobileMe email account does not automatically configure in Outlook for Mac 2011 after the Office for Mac 2011 SP2 update

For MobileMe accounts, use the following settings for the incoming and outgoing servers:

Incoming server: mail.me.com

Outgoing server: smtp.me.com

For iCloud accounts, use the following settings for the incoming and outgoing servers:

Incoming server: imap.mail.me.com

Outgoing server: smtp.mail.me.com

Can’t sync Outlook for Mac with calendars and contacts in iCloud account

Outlook for Mac 2011 does not currently support CalDAV or CardDAV. This means that it is not possible to synchronize your iCloud calendar or contacts with Outlook for Mac. However, Outlook for Mac 2011 does support iCloud Mail. For more information, see Microsoft Outlook for Mac 2011 compatibility with Apple iCloud

Can’t sync Outlook for Mac with Outlook.com folders

With POP and IMAP e-mail accounts, e-mail messages are the only items that are synchronized between Outlook and the mail server. Other items that you create in Outlook— such as contacts, calendar events, tasks, and notes— are stored on your computer, not on the mail server.

Can’t sync Outlook for Mac with calendars in Gmail

Outlook for Mac 2011 does not currently support CalDAV. This means that it is not possible to synchronize your Gmail calendar with Outlook for Mac.

Can’t import mail from Apple Mail in Mac OS X v10.7 (Lion)

If you are on Mac OS X v10.7 (Lion), you cannot import from Apple Mail into Outlook for Mac 2011.

Outlook for Mac does not support a way to replace signatures

Outlook for Mac does not automatically support a way to replace a signature with another signature in the e-mail message. When you add a new signature in an attempt to replace an old one, Outlook for Mac appends the new signature instead of replacing it. To replace the signature, you must manually delete the original signature from the e-mail message.

Cannot change the color of shared calendars in Outlook for Mac

It's not possible to change the color for shared calendars in Outlook for Mac.

Cannot resize pictures attached to messages

You need to resize pictures before adding to Outlook.

Outlook cannot open hyperlinks that don’t include a full URL

A hyperlink that is inserted into an e-mail message must be a full URL address that includes http://, otherwise the recipient cannot open the link.

E-mail messages disappear

If you rename or move the Microsoft User Data folder or any of its subfolders, Outlook is unable to find your identity and a new, blank identity is created.